Ameresco, Inc. Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments on the Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Designated \| Interest rate swap instruments \| Other assets
Derivatives, Fair Value [Line Items]
Asset derivatives	$ 255	$ 703
Designated \| Interest rate swap instruments \| Other liabilities
Derivatives, Fair Value [Line Items]
Liability derivatives	3,990	3,187
Not Designated \| Interest rate swap instruments \| Other assets
Derivatives, Fair Value [Line Items]
Asset derivatives	30	30
Not Designated \| Commodity swap contracts \| Other assets
Derivatives, Fair Value [Line Items]
Asset derivatives	33	33
Not Designated \| Commodity swap contracts \| Other liabilities
Derivatives, Fair Value [Line Items]
Liability derivatives	70	70
Not Designated \| Interest make-whole provisions \| Other liabilities
Derivatives, Fair Value [Line Items]
Liability derivatives	$ 1,085	$ 1,808